Enhanced crude oil recovery method and system

ABSTRACT

An enhanced crude oil recovery method comprises:
         injecting steam into a steam injection conduit ( 5 ) which is retrievably arranged in a steam injection well ( 1 );   inducing the steam to flow from the interior of steam injection conduit ( 5 ) through gradually widening steam injection channels ( 6 ) traversing the wall of the conduit ( 5 ) into the surrounding formation ( 2 ); and   producing crude oil heated by the injected steam from the formation ( 2 ).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent Application 08164817.2 filed Sep. 22, 2008, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to an enhanced crude oil recovery method and system, wherein steam is injected into a crude oil containing underground formation for enhancing crude oil production therefrom.

Such a method and system are known from U.S. Pat. No. 6,158,510. In the system known from this prior art reference a steam injection conduit with radial steam injection holes is arranged within a blank section of a well liner, such that steam is injected radially into the annular space between the steam injection conduit and the well liner and is then deflected to perforated sections of the well liner, that are surrounded by sandscreens, through which the steam is injected from the annular space into the surrounding formation.

A disadvantage of the known system is that the radial steam injection holes and surrounding blank section of the well liner are prone to erosion and corrosion by the flux of hot steam, in particular if the steam injection conduit is not co-axial to the well liner, and that it is difficult to maintain a substantially equal steam flux through each of the holes at varying conditions.

It is an object of the present invention to alleviate these disadvantages and to provide a retrievable and reconfigurable steam injection system and method in which steam injection channels can be configured such that erosion of the channels is reduced and such that an accurately determined and constant flux of steam can be injected through the channels into the surrounding formation.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an enhanced crude oil recovery method, comprising:

-   -   injecting steam into a steam injection conduit which is         retrievably arranged in a steam injection well;     -   inducing the steam to flow from the interior of steam injection         conduit through gradually widening steam injection channels         traversing the wall of the conduit into the surrounding         formation; and     -   producing crude oil heated by the injected steam from the         formation.

The steam injection conduit may be substantially coaxial to a surrounding at least partially permeable well liner such that an substantially annular space is present between the conduit and liner, in which space an annular seal may be arranged at a location between the wellhead and the gradually widening steam injection channels.

In accordance with the invention there is furthermore provided a steam injection system comprising gradually widening steam injection channels traversing the wall of a steam injection conduit, which is configured to be retrievably arranged within a steam injection well and to inject steam into a formation surrounding the well.

Each gradually widening steam injection channel preferably comprises:

-   -   a tubular inflow section in which a tubular steam injection         nozzle is arranged; and     -   an expansion section, which intersects the tubular inflow         section and provides a steam expansion chamber for conveying         steam from the nozzle into a space between the outer surface of         the steam injection conduit and the inner surface of a at least         partially permeable well liner which is arranged within the         steam injection well.

It is furthermore preferred that:

-   -   each gradually widening steam injection channel is arranged in a         side pocket in a thick walled section of the steam injection         conduit, which has a smaller internal width than adjacent         sections of the steam injection conduit;     -   the tubular inflow section of each steam injection channel is         drilled from an end face of the thick walled section through the         wall of the thick walled section in a direction substantially         parallel to the longitudinal axis of the steam injection         conduit;     -   the expansion section of each steam injection channel is         machined from the outer surface of the thick walled section such         that it intersects the tubular inflow section; and     -   the expansion section has a central axis which intersects or         crosses the longitudinal axis of the steam injection conduit at         an acute angle between 6 and 60 degrees relative to the         longitudinal axis.

These and other features, embodiments and advantages of the method and/or system according to the invention are described in the accompanying claims, abstract and the following detailed description of preferred embodiments disclosed in the accompanying drawing in which reference numerals are used which refer to corresponding reference numerals that are shown in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic longitudinal sectional view of a steam injection well, which is equipped with steam injection system according to the invention.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENT

FIG. 1 shows a steam injection well 1, which comprises a substantially horizontal lower section that traverses a viscous crude oil containing underground formation 2.

The depicted lower section of the well 1 comprises a at least partially permeable well liner 3, which comprises a series of perforations 4 and contains a retrievable steam injection conduit 5.

The conduit 5 comprises a series of gradually expanding steam injection channels 6 for conveying steam from the interior of the steam injection conduit 5 into the annular space 7 between the steam injection conduit 5 and well liner 3. The steam injection channels 6 are arranged in thick walled sections 5A of the steam injection conduit 5, which each have a smaller internal width than adjacent large diameter sections 5B and 5C of the steam injection conduit. Each steam injection channel 6 comprises a longitudinal tubular inflow section 6A, which is drilled from an end face 9 of the thick walled section 5A through the wall of the thick walled section 5A in a direction substantially parallel to the longitudinal axis 8 of the steam injection conduit 5.

A steam injection nozzle 6B is inserted within each longitudinal tubular inflow section 6A.

Each steam injection channel 6 furthermore comprises and an inclined expansion section 6C, which provides a steam expansion chamber and which is machined from the outer surface of the thick walled section 5B such that a central axis 10 of the expansion section 6C intersects a central axis 11 of the longitudinal tubular inflow section 6A at an acute angle α.

Each expansion section 6C has a central axis 10 which is intersects or crosses the longitudinal axis 8 of the steam injection conduit 5 at an acute angle α between 6 and 60 degrees. In the embodiment shown the steam injection conduit 5 is substantially coaxial to the well liner 3 so that the longitudinal axis 8 of the steam injection conduit 5 substantially coincides with the longitudinal axis of the well liner 3. In the embodiment shown the steam injection nozzle is oriented substantially co-axial to the longitudinal axis 8 of the steam injection conduit 5 and the angle α is shown as the angle between the central axis 11 of the steam injection nozzle and the central axis 10 of the expansion section 6C of each steam injection channel 6. A seal 12 is arranged in the substantially annular space 7 between the steam injection conduit 5 and the well liner 3 at a location between the wellhead (not shown) and the series of gradually widening injection channels 6. Optionally additional seals are arranged in the annular space 7 between adjacent steam injection channels 6.

Optionally the expansion section 6C may be arranged within a blank section of the well liner 3, such that steam is injected at an acute angle α into the annular space between expansion section 6C and the well liner 3 and is then deflected to perforations 4 in the well liner 3, that are surrounded by sandscreens (not shown), through which the steam is injected from the annular space into the surrounding formation 2. 

1. An enhanced crude oil recovery method, comprising: injecting steam into a steam injection conduit which is retrievably arranged in a steam injection well; inducing the steam to flow from the interior of steam injection conduit through gradually widening steam injection channels traversing the wall of the conduit into the surrounding formation; and producing crude oil heated by the injected steam from the formation.
 2. The method of claim 1, wherein each gradually widening steam injection channel comprises: a tubular inflow section in which a tubular steam injection nozzle is arranged; and an expansion section, which provides a steam expansion chamber for conveying steam from the nozzle into a space between the outer surface of the steam injection conduit and the inner surface of a at least partially permeable well liner which is arranged within the steam injection well.
 3. The method of claim 1, wherein each gradually widening steam injection channel is arranged in a side pocket in a thick walled section of the steam injection conduit, which has a smaller internal width than adjacent sections of the steam injection conduit; the tubular inflow section of each steam injection channel is drilled from an end face of the thick walled section through the wall of the thick walled section in a direction substantially parallel to the longitudinal axis of the steam injection conduit; and the expansion section of each steam injection channel is machined from the outer surface of the thick walled section such that it intersects the tubular inflow section.
 4. The method of claim 3, wherein the expansion section has a central axis which intersects or crosses the longitudinal axis of the steam injection conduit at an acute angle between 6 and 60 degrees relative to the longitudinal axis.
 5. The method of claim 4, wherein the steam injection conduit is substantially coaxial to a surrounding at least partially permeable well liner such that a substantially annular space is present between the conduit and liner, in which space an annular seal is arranged at a location between a wellhead of the steam injection well and the gradually widening steam injection channels.
 6. The method of claim 5, wherein the method further comprises converting the produced crude oil into a transportation fuel and/or other chemical end products.
 7. An enhanced crude oil recovery system comprising gradually widening steam injection channels traversing the wall of a steam injection conduit, which is configured to be retrievably arranged within a steam injection well and to inject steam into a formation surrounding the well.
 8. The system of claim 7, wherein each gradually widening steam injection channel comprises: a tubular inflow section in which a tubular steam injection nozzle is arranged; and a expansion section, which intersects the tubular inflow section and provides a steam expansion chamber for conveying steam from the nozzle into a space between the outer surface of the steam injection conduit and the inner surface of a at least partially permeable well liner which is arranged within the steam injection well.
 9. The steam injection system of claim 8, wherein each gradually widening steam injection channel is arranged in a side pocket in a thick walled section of the steam injection conduit, which has a smaller internal width than adjacent sections of the steam injection conduit; the tubular inflow section of each steam injection channel is drilled from an end face of the thick walled section through the wall of the thick walled section in a direction substantially parallel to the longitudinal axis of the steam injection conduit; and the expansion section of each steam injection channel is machined from the outer surface of the thick walled section such that it intersects the tubular inflow section.
 10. The steam injection system of claim 9, wherein the expansion section has a central axis which intersects or crosses the longitudinal axis of the steam injection conduit at an acute angle between 6 and 60 degrees relative to the longitudinal axis. 